1. Field of the Invention
The present invention relates generally to an automotive four wheel drive train which includes a transfer gear via which engine drive output is distributed to the forward and rear wheels and more specifically to a four wheel drive train which enables the engine, clutch and transfer gear to be disposed at one end of the vehicle and the transmission to be located at the other end, and thus improves the vehicular weight distribution.
Description of the Prior Art
It is well known that in order to improve the overall handling characteristics of a vehicle it is advantageous to distribute the weight of the drive train evenly between the forward and rear axles.
One attempt to achieve the above mentioned type of weight distribution in a high performance vehicle has been to dispose the engine at the front of the vehicle, dispose the clutch, transmission and final drive (which are arranged in that order) at the rear, and interconnect the engine and the clutch with a propeller shaft which is housed in a torque tube.
While this has met with success in pure F-R type gear trains, adapting this concept to 4 WD type drive trains has encountered some difficulties in that it is necessary to add a transfer gear and to connect this with the front final drive.
A 4 WD arrangement of the above mentioned nature is disclosed in JP-A-62-247924. However, in this instance a number of drawbacks are encountered. That is to say, the propeller shaft which interconnects the transfer gear at the rear of the vehicle with the front final drive becomes excessively long. Further, the propeller shaft is offset to one side of the vehicle center line and thus tends to broaden the tunnel which ends through the vehicle cabin to an undesirable degree.
JP-A-61-157437 discloses another prior art four wheel drive train which is also based on an F-R drive arrangement. In this arrangement the engine, transmission, transfer and front final drive are disposed at the front of the vehicle, while the rear final drive is disposed at the rear of the same. The engine torque is transferred directly to the front wheels and to the rear wheels via a transfer clutch.
However, with this type of prior art four wheel drive train, as the engine, transmission, transfer and front final drive are disposed at the front of the vehicle chassis and only the rear transfer is disposed at the rear, the distribution of the weight with respect to the front and rear axles of the vehicle is such that a disproportionate amount is located near the front axle. As a result, the desired weight distribution is not achieved and the handling characteristics of the vehicle tend to be accordingly impaired.
Thus, as will be appreciated, in the case it is desired to adapt basic F-R or F-F type drive trains to provide 4WD, it is necessary to contrive a position for the transfer and the propeller shaft or shafts. For example, in the prior art when the transfer is connected to the transmission output shaft with normal techniques wherein the transfer is disposed toward the rear of the chassis, the propeller shaft which extends from the transfer to the front final drive must be extremely elongated and at the same time positioned not to interfere with the engine.